Herpes simplex virus (HSV) is widespread in the human population, and is considered a classic example of a "latent" virus. Two major forms of infection are recognized. Primary or systemic HSV infection occurs in individuals lacking antibodies to HSV. Recurrent HSV infection, believed to result from activation of "latent" virus, occurs at localized sites in individuals expressing antibodies. A third form, which occurs at a lower frequency, is seen in previously infected individuals whose immune system is compromised, thus allowing virus replication and systemic infection.
Two types of HSV are recognized; HSV-1, which usually is associated with infections in the oral region, and HSV-2, which usually is associated with infections in the genital region. Although antibodies generated against HSV-1 and HSV-2 show extensive intertypic cross-reactivity (see Hampar et al., J. Immunol., Vol. 104, p 593 (1970)), the two virus types can be distinguished by their antigenic profiles and by their genetic composition. While most adults express protective antibodies against HSV, primary or systemic infection can pose a serious problem. In newborns, for example, a potentially fatal infection can occur following transmission of virus from mothers with an active recurrent genital infection. During the past 20 years, in fact, the incidence of neonatal HSV infection has increased significantly in parallel with the increased incidence of genital HSV infection in pregnant females (approximately a nine-fold increase from 1966 to 1979). Systemic HSV infection during pregnancy is also potentially dangerous to the mother.
The recommended procedure for a pregnant woman suspected of harboring a genital HSV infection is to perform weekly tests to determine whether infectious virus is being released into the birth canal. This is a costly and insensitive procedure, however, and its use is limited to the high risk category of pregnant women who show either (i) a history of recurrent genital HSV infection, (ii) active disease during pregnancy, or (iii) sexual partners with proven genital HSV infection. If an active infection is apparent, a cesarean delivery, with its associated risks, is performed to protect the newborn. Unfortunately, approximately 70% of neonates with HSV infection are born of women with no clinical signs or symptoms of active disease. Consequently, the availability of a rapid, reliable and inexpensive serological test for identifying women harboring HSV-2 is needed.
Infection by HSV-1 and HSV-2 can occur in any area of the body. While recurrent infection in the genital area usually involves HSV-2, the high incidence of HSV antibodies in the adult population is primarily due to HSV-1, which usually is associated with oral infections. While HSV-1 and HSV-2 are closely related antigenically, a number of serological tests have been developed for differentiating between antibodies directed against the two virus types.
These tests include, inter alia, neutralization kinetics (NK), multiplicity analysis NK, microneutralization (MN), modified MN, indirect hemagglutination, immune lysis of infected cells, radioimmunoassay using purified viral proteins, immunoelectrophoresis, radioimmunoprecipitation-polyacrylamide gel electrophoresis, and enzyme-linked immunosorbent assay (ELISA). The MN and modified MN tests are the most widely used tests for distinguishing between antibodies directed against HSV-1 and HSV-2, and are considered the standard against which any new test should be compared.
In intital attempts to develop an ELISA test for distinguishing between antibodies directed against HSV-1 and HSV-2, it was assumed from other studies that the 130,000 mw glycoprotein C (gC) was antigenically specific for HSV-1. Initial attempts were unsuccessful, however, since positive ELISA reactions were consistently observed when HSV-2 specific antisera were tested against affinity purified gC. It was subsequently shown that gC was not specific for HSV-1, but was antigenically cross-reactive and mapped at a position colinear with the 75,000 mw glycoprotein F (gF) of HSV-2 (see Zweig et al., J. Virol. Vol. 47 p 185 (1983)). Glycoprotein gD is 110,000 mw. A confirmed antigenically type-specific protein has not been described for either HSV-1 or HSV-2. The present invention is designed to develop an immunoassay method which can be used effectively for differentiating antibodies directed against HSV-1 and HSV-2 in human sera. The results of these efforts comprise the invention described herein.